The present invention relates to a method and apparatus of forming a thin functional film. In the present invention, the thin functional film is intended to mean one of various materials (for example an organic compound) in the form of a thin film attached onto an object by vapor deposition for the purpose of providing one of various functions such as recording information, displaying information, adjusting or changing of an optical property, converting energy and the like. Particularly, the following thin films are exemplified: a thin film information recording layer comprising an organic dye (or pigment) material which is formed on a substrate of an optical recording medium; a thin film of a sensitization material for a photoelectric conversion element which is formed on a substrate of a solar cell panel; and a charge transportation layer of an OPC (optical photo conductivity) material on a photoconductor drum.
Presently, various functional films are used widely for information recording elements (such as an optical recording medium and a photoconductor drum), information displaying elements (such as a color filter and a thin electroluminescence panel) as well as energy conversion elements (such as a solar cell) and medical diagnosis elements. Those functional films are all formed by a wet method such as spin coating or a dry method such as vacuum vapor deposition or sputtering.
Particularly, one example of optical recording mediums that has been recently noted is the recordable optical disk (CD-R), in which an information recording layer is formed on a substrate using an organic dye material since signals are conveniently read out from the organic dye material using a CD player or a CD-ROM drive. Hitherto, the recording layer has been formed by a wet method in which a solution of the organic dye material is applied onto the substrate by spin-coating followed by drying. In order to produce a satisfactory optical recording medium, know-how and skills are required since tolerable ranges of production are narrow.
On the other hand, the dry method of forming the recording layer has been also attempted in which vacuum vapor deposition is used so as to relatively easily produce a thin functional film having uniform thickness and uniform optical properties. For example, Japanese Patent Kokoku Publication No. 8-13572 disclosed an optical recording medium which is produced by heating a molybdenum boat containing a phthalocyanine based organic dye material so as to evaporate the material, and depositing the evaporated material onto a substrate surface to form a thin film of the organic dye material as a recording layer on the substrate. Further, an example of an apparatus which carries out such vapor deposition is disclosed in Japanese Patent Kokoku Publication No. 7-62249.
However, the vacuum vapor deposition as described above has a problem in that bumping and splashing often occur when the organic dye material in the boat is heated, which likely creates defects in the formed thin film due to inclusion of pinholes in the thin film. Such a problem should be resolved in order to make the deposition method industrially effective. Such a problem is not limited to the case in which the information recording layer is formed by the vacuum vapor deposition. Furthermore, it is a common problem in cases in which various materials are evaporated and deposited onto objects for the formation of various thin functional films.
It is an object of the present invention to provide a method and an apparatus for forming a uniform thin functional film having fewer defects so as to alleviate and preferably substantially overcome such a problem. It is noted that although the method and the apparatus according to the present invention are explained as examples with reference to a case in which a recording layer as the thin functional film is formed by depositing a dye material onto a substrate for an optical recording medium, the present invention is applicable to the formation of the other various thin functional films.
In the present invention which achieves the above mentioned object, a material, from which a thin functional film is formed (which is also referred to as a xe2x80x9cfunctional materialxe2x80x9d), is placed preferably in an evaporation vessel and heated under a reduced pressure (preferably at a highly vacuum pressure) so as to evaporate the material, and the evaporated material is deposited onto an object, such as a substrate, so that a thin functional film is formed thereon, characterized in that the functional material is heated and evaporated from above, whereby the thin functional film is formed on the substrate.
According to the present invention, a thin functional film having a high quality is formed with notably reduced defects such as pinholes.
That is, the present invention provides a method for forming a thin functional film by evaporating a functional material under a reduced pressure condition and depositing the evaporated material onto an object, characterized in that the functional material is placed preferably in an evaporation vessel and heated from a position above the functional material so that the functional material is evaporated.
In addition, the present invention provides an apparatus for forming a thin functional film by evaporating a functional material under a reduced pressure condition and depositing the evaporated material onto an object, characterized in that the apparatus comprises an evaporation vessel which receives the functional material from which the thin functional film is formed, and a heating means which heats the functional material from a position above the functional material placed in the evaporation vessel.